Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be possible otherwise to do so. Artificial joints usually comprise metal, ceramic and/or plastic components that are fixed to existing bone.
Such joint replacement surgery is otherwise known as “joint arthroplasty”. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto.
Many designs and methods for manufacturing implantable articles, such as bone prostheses are known to exist. Such bone prostheses include components of artificial joints, such as elbows, hips, knees and shoulders.
Currently, in total hip arthroplasty, a major critical concern is the instability of the joint. Instability is associated with dislocation. Dislocation is particularly a problem in total hip arthroplasty.
Factors related to dislocation include surgical technique, implant design, implant positioning and patient related factors. In total hip arthroplasty, implant systems address this concern by offering a series of products with a range of lateral offsets, neck lengths, head lengths and leg lengths. The combination of these four factors affects the laxity of the soft tissue. By optimizing the biomechanics, the surgeon can provide a patient a stable hip much more resistant to dislocation. In order to accommodate the range of patient and anthropometrics, a wide range of hip implant geometries are currently manufactured by DePuy Orthopaedics, Inc., the assignee of the current application and by other companies. In particular, the S-ROM® total hip systems offered by DePuy Orthopaedics, Inc. include three offsets, three neck lengths, four head lengths and one leg length adjustment. The combination of all these biomechanic options is rather complex.
Anteversion of a hip stem is closely linked to the stability of the joint. Improper version can lead to dislocation and patient dissatisfaction. Version control is important in all hip stems. However, it becomes a more challenging issue with the advent of stems with additional modularity.
The prior art has provided for some addressing of the anteversion problem. For example, the current S-ROM® stems have laser marking on the medial stem and the proximal sleeve. This marking enables the surgeon to measure relative alignment between these components. Since the sleeve has infinite anteversion, it is not necessarily oriented relative to a bony landmark that can be used to define anteversion. In fact, the sleeves are sometimes oriented with the spout pointing directly laterally into the remaining available bone.
Prior art stems may be aligned relative to patient's bony landmarks. These stems are monolithic stems. They cannot locate the neck independently of the distal stem. Therefore, the anteversion is limited. Most bowed, monolithic stems are sold in fixed anteversion. For example, at an anteversion of 15°, these monolithic stems have limited flexibility for rotational alignment since the distal stem must follow the bow of the patient's femur and this may not provide an optimal biomechanical result. Thus, a need for an instrument as well as implants that provide for anteversion alignment relative to a patient's bony landmark exists.